1. Field
Embodiments of the present invention generally relate to an apparatus capable of generating uniform plasma across and beyond the peripheral edge of a substrate.
2. Description of the Related Art
In substrate processing applications, a substrate is placed on a substrate support in a process chamber and exposed to an energized gas to deposit or etch material on the substrate. The support may comprise an electrostatic chuck with at least one electrode that may be electrically charged to electrostatically hold the substrate on the support. The electrode may also be electrically biased, for example with high frequency electrical power, such as radio frequency (RF) power, to energize process gas provided in the chamber to process the substrate.
In a typical process chamber, a gas distribution device introduces process gas into the chamber. The gas is energized into plasma by applying an RF voltage to an electrode, such as a cathode, within a substrate support, such as an electrostatic chuck, and by electrically grounding an anode to form a capacitive field in the process chamber. A substrate may be electrically biased with respect to the cathode, such as by applying a direct current to the cathode, and an electrostatic force generated to attract and hold the substrate on the electrostatic chuck. The substrate is processed by the plasma generated within the process chamber.
During processing, the substrate support surface, such as the surface of the electrostatic chuck, is subjected to plasma and ion bombardment within the processing chamber. Over time, the plasma and ion bombardment may damage portions of the electrostatic chuck. To protect the chuck and increase its lifetime, a process kit is positioned around the electrostatic chuck within the processing chamber. The process kit typically includes an annular ring that covers the upper portion of the electrostatic chuck that is exposed to the plasma.
FIG. 1 is a cross-sectional view of a prior art electrostatic chuck 100 with an annular ring 108 installed. The electrostatic chuck 100 includes an annular flange 102, which supports the annular ring 108. The annular ring 108 is typically comprised of an insulating or dielectric material, such as a ceramic material. The primary purpose of the annular ring is to prevent the plasma in the processing chamber from contacting and eroding the electrostatic chuck 100.
The electrostatic chuck 100 includes a chucking surface 106 for supporting and retaining a substrate 130 to be processed. A cathode 120 is positioned within the electrostatic chuck 100 near the chucking surface 106. A central conductor 195 supplies DC voltage to the cathode 120 for retaining the substrate 130. The central conductor 195 also supplies RF voltage to the cathode 120 for capacitively energizing a process gas into plasma for processing the substrate 130.
As can be seen in the configuration depicted in FIG. 1, the cathode 120 is located near the chucking surface 106 for generating adequate electrostatic force required to retain the substrate 130. As such, the cathode 120 is located within the portion of the chuck 100 that is circumscribed by the annular ring 108. Therefore, the peripheral portion of the cathode 120 is radially terminated near or within the periphery of the substrate 130. It has been discovered that this configuration leads to non-uniformity in the RF field generated by the cathode 120 resulting in undesirable non-uniformities in the peripheral edge of the substrate 130.
Accordingly, a need exists for an electrostatic chuck capable of providing uniform plasma across the substrate surface, and in particular, across the peripheral edge of the substrate. A further need exists for an electrostatic chuck capable of providing uniform plasma beyond the peripheral edge of the substrate.